Now known as lost wax casting Casting is a cutting or no cutting of the casting process less foundry industry is a superior technology, which is widely used. It is not only applicable to all types, all kinds of alloy casting, casting and production of dimensional accuracy, surface quality is higher than other casting methods, and even other casting methods difficult to cast complex, high temperature, easy to machining castings, casting can be employed to cast.
Casting was developed in ancient wax casting basis. As ancient civilizations, China is one of the countries using this technology earlier, far away in a few centuries BC, the ancient working people of this country to create a lost wax casting technique for casting with a variety of fine patterns and text the tripods and utensils and other products, such as the Spring and Autumn Period tomb statue disk and so on. Tomb statue base plate for multiple intertwined dragons, they are end to end, staggered up and down, to form an intermediate hollow multilayer moire-like pattern, the pattern is difficult by conventional casting process produced, but with the lost wax casting method process, you can use paraffin strength, easy carving characteristics, with ordinary tools can be carved out of the tomb to get the same respect dish paraffin material crafts, then additional gating system, paint, dewaxing, casting, you can get beautiful tomb respect dish.
Modern investment casting methods in the practical application of industrial production in the 1940s. At that time the development of jet engines, require manufacturers such as blades, impellers, nozzles and other complex shape, size, precision and smooth surface of the heat-resistant alloy parts. Because of heat-resistant alloy machining difficult, complex shape parts that can not or difficult to use other methods of manufacture, and therefore, need to find a new precision molding process, so learn handed down from ancient lost wax casting, through the materials and workmanship improvements, modern investment casting method to obtain an important development on the basis of the ancient craft. Therefore, the development of the aviation industry to promote the application of investment casting, investment casting and continuous improvement and perfection, but also for the aviation industry to further improve performance and create favorable conditions.
Our country is in the 1950s and the beginning of the sixties the investment casting used in industrial production. Later this advanced casting process has been tremendous development, have been widely used in the aerospace, automotive, machine tools, ships, internal combustion engines, gas turbines, telecommunications equipment, weapons, medical equipment and tools and other manufacturing industries, as well as for process manufacturing and crafts of.
The so-called investment casting process, it simply is to use fusible material (such as wax or plastic) fusible model (referred to as the melting mold or model), which is coated in several layers of a special fire-resistant coating, after drying and hardening after the formation of a whole shell, then steam or hot water from the shell model of melt away, and then placed in the sand box shell, filled with dry sand around it in shape, and finally cast into the roaster in the high temperature roasting, after the mold or shell after roasting, in which molten metal is poured to obtain castings (such as the use of high-strength shell, and the shell may not have direct roasting shape after stripping).
Size high precision castings, generally up CT4-6 (sand casting for the CT10 ~ 13, die-casting for CT5 ~ 7), of course, due to the investment casting process is complex, factors affecting precision casting size more, such as mold material shrinkage, melting mold deformation, the amount of change in the shell line heating and cooling process, the contraction of the alloy during solidification and deformation during the casting, etc., so the ordinary investment castings, although the dimensional accuracy is high, but its still need to improve consistency (using the high-temperature wax casting size consistency to improve the lot).
Suppression of melting mold cavity surface finish using a high-pressure, therefore, melting mold surface finish is relatively high. In addition, the shell and refractory by a special high temperature resistant adhesive formulated into a refractory coating applied hung on melting mold made, the cavity surface in direct contact with the molten metal finish. Therefore, the surface finish of castings higher than the general castings, generally up Ra.1.6 ~ 3.2μm.
Investment Casting biggest advantage is due to the castings have high dimensional accuracy and surface finish, it can reduce the machining work, but in the higher parts of the site can stay a little allowance, and even some casting only keep grinding, polishing margin, do machining can be used. Thus, the use of investment casting method can save a lot of machine tools and machining time, significant savings metal raw materials.
Another advantage of the method of investment casting is that it may be cast complex castings of various alloys, particularly may be cast superalloy castings. Such as jet engine blades, its sleek outline and cooling cavity, with the machining process is almost impossible to form. Investment casting process to produce not only mass production can be done to ensure the consistency of the casting, and avoid stress concentration of residual knife pattern after machining.
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